Party line connector circuit for code ringing



Jan. 29, 1952 Filed Jan. 21, 1948 3. E. LOMAX PARTY LINE CONNECTORCIRCUIT FOR CODE RINGING CONNECTOR 200 3 Sheets-Sheet 2 TEST | 252 ,/2e5W V 3246 RING REV R250 0 M2l8 240 43 N [ELE M2|6 v zewf s24s\ o 2 T 274RLSE d o0 1 0 o I M.S. ON

. ZLLTJJJB O T 270 TO RING. c005 INT. 5275 INVENTOR. Clarence E. Lomox FIG. 2 I

Aftys.

Jan. 29, 1952 c, LOMAX 2,583,782

PARTY LINE CONNECTOR CIRCUIT FOR CODE RING ING Filed Jan. 21, 1948 3Sheets-Sheet 5 CONNECTOR 20o m 34 (I! LINE CIR 355 PBX, 350 d o\ LINECIR. 356 I 340 0* 352M1- 6 34: 353 w Q1) 04 0 7 98 332 2 F my,

CTORS LC 361 0 rz LQ 38| LC. I 9 39IBB 391F F EA!3QIB!39IC Ffi ih 5% rI. g

NP 3m gems 237m A 3m; 4 $316; T

INVENTOR. Clarence E. Lomox FIG. 5 BY Y I M Ow q Qawd,

Attys.

Patented Jan. 29, 1952 PARTY LINE CONNECTOR CIRCUIT FOR CODE RINGINGClarence E. Lomax, Chicago, Ill., assignor to Automatic ElectricLaboratories, Inc., Chicago, 111., a corporation of Delaware ApplicationJanuary 21, 1948, Serial No. 3,424

9'Olaims. 1

The present invention relates to automatic telephone systems, and moreparticularly to connector switches for such systems.

It is an object of the present invention to provide in an automatictelephone system, including both a group of trunks and a plurality ofparty subscriber lines, a connector switch incorporating combinationtrunk-hunting and ringing control facility.

Another object of the invention is to provide an automatic switchincorporating improved divided ringing control facility.

A further object of the invention is to provide in an automatic switchhaving access to a party subscriber line via two paths, an improvedarrangement responsive to the path over which the party subscriber lineis selected by the switch for selectively determining the divided ringincircuit to be utilized in projecting ringing current over the selectedparty subscriber line.

Further features of the invention pertain to the particular arrangementof the circuit elements of the connector switch; whereby theabove-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation,together with further objects and advantages thereof, will best beunderstood by reference to the folowing specification taken inconnection with the accompanying drawings, in which Figures 1 to 3,inclusive, taken together illustrate the details of an automatictelephone system having incorporated therein the features of the presentinvention. Specifically Figs. 1 to 3, inclusive, should be arranged inupstandin side-by-side relation from left to right in order to form aunified diagram.

, Referring now more particularly to Figs. 1 to 3, inclusive, of thedrawings, there is illustrated an automatic telephone system comprisingtwo exchanges I and 2|] interconnected by a group of trunk, lines,including the trunk line I26, respectively terminating in trunk circuitsdisposed in the exchanges I0 and 20; the trunk line I26 terminating inthe trunk circuits I25 and I21 respectively disposed in the exchangesIll and 20.

The exchange I0 serves a group of private subscriber lines, includingthe private subscriber line I05; the private subscriber substation TIUIbeing connected to the private subscriber line I05. Also the exchangeIll serves a number of roups of private branch exchange trunks, one ofthe groups including the three private branch exchange trunks 35I 352and 353 to which the private branch exchange 350 is connected. Alsoscriber lines, including the party subscriber line 1 38I to which tenparty subscriber substations 38IA, 38IB, etc., are connected; the partysubscriber line 38I being of the ground return type.

Further the exchange It serves a fourth group of party subscriber lines,including the party subscriber line 39I to which twenty party subscribersubstations 39IA, 35IB, etc., and 39IAA, 39IBB, etc., are connected; theparty subscriber line 39I being arranged for divided ringing. Finally,the exchange I0 serves the group of trunk lines, including the trunkline I26 extending between the exchanges I0 and 20.

Further in the exchange I0, the private subscriber lines I05, etc., areprovided with individually associated line circuits III], etc.; theparty subscriber'lines 36I, 31I, 3BI, 39I, etc., are provided withindividually associated line circuits 362, 312, 382, 392, etc.; and theprivate branch exchange trunks 35I, 352, 353, etc., are provided withindividually associated line circuits 354, 355, 356, etc. Also theexchange I0 comprises a plurality of finder-connector links, one ofwhich is illustrated as comprising the finder I I5 and the connector200, and an associated distributor IIZ operatively connected between thevarious links and the various line circuits III], etc. In the exchangeIn each private subscriber substation TIOI, etc., and each partysubscriber substation 36IA, 38IA, 391A, etc., are provided withconventional substation apparatus including a transmitter, a receiver, adial and a ringer. Also, the P. B. X 350 is provided with conventionalapparatus includin an attendants cabinet. Finally, the line circuits H0,362, 312, 382, 392, 354, 355, 356, etc., as well as the distributor II2,are of any suitable types. Moreover the trunk circuits I25, etc., andI21, etc., in the respective exchanges I0 and 20 are of any suitabletype.

Preferably, the finders I I5, etc., are of the conventional Strowgertype and have access to the variousprivate subscriber lines I05, etc.,tothe variousparty subscriber lines 36I, 31I, 3BI1. 39L

r 3 etc., and to the private branch exchange trunks 35!, 352, 353, etc.Similarly, the, connectors 200, etc., have access to the privatesubscriber lines "35, etc., to the party subscriber lines/36!, SH, 38!,39!, etc., to the private branch exchange trunks 35!, 352, 353, etc.,and to the trunk lines !26, etc.

The exchange was of; the automatic type and serves a number ofsubscriber lines, including the private subscriber line !29 to which theprivate subscriber substation T!3! is connected. The private subscriberlines I29, etc., are provided 7 V with individually associated linecircuits !30, etc.

Further the automatic exchange -comprises an associated with the trunkcircuits !2'!, etc., and; having access to'the private subscriber lines!29,

automatic switch train !28 of ans/"suitable. type etc.

identical to the connector 20!], which comprises, as shown in Figs. 1 to3, inclusive, a relay group,- including a switch relay RMILa line relayR! 5!), a transfer relay R160, ahold relay Rl 'lll a backbridge relayR2"), a pick-up relay RZZIL; a ring cut-off relay R238, a ring reverserelay R240, a

rotary step relay R256,a test relay R260, a series relay R3!,0, a ;seriesslave relay R320, and a switch-through relay R33i}. Also theconnector 7 200i comprises a Strgwgerjmechanism 310;,iricludingfourindividual wipers 3 4! ,,342, 343 and 3%, a vertical magnet .MIBBfor driving the wiper carriage, step bystepin the verticaldirection awayfrom its normal'vertical position, a rotary In the exchange I0 each ofthe connectQrsis.

magnet M218 for driving thetwiper carriage step by step inthe rotarydirection away from its normal rotary i nrand ar lease a net M218 forreleasing the wiper carriage and for causing it to be' returned to itsnormal rotary and vertical positions. Also associated' with the wipercarriage a e a m b r f sated S t r t' 3'5 Sm, 2 248 ...s i nd smwnwn a epperated in response to various operations of the wiper carriage oi theStrowger mechanism 340.

e i cally, t ecse itch priheswnd S246 are operated when thewipercarriage ot ow er mechan m 40 ,is s i e ne s ep. i the verticaldirection away from its normal vertical position the setsofswitchsprings S3l5 and:

15a? per ed whenih wi ersar e f he Strowger mechanism 351]!) is driyeninthe vertical;

direction to the tenth level inthe associated contact bank in which thetrunk -linesl26, etc,,

are terminated; the switch Springs S243iandf$3l5 are operated when thewiper carriage of the Strowger mechanism 349 is driven in the verticaldirection to the ninth level in the associatedcontact bank inwhichqtheprivate, branch exchange trunks 35!, 352 and 35.3 areterminated; andthe set of switch springs S2 4! is operated when thewiper carriage of the Strowgermechanisrn 340 is driven in the verticaldirection to the levelin the associated contact bankinwhich the fourthgroup of party subscriber lines 39 !,,etc are terminated. Also in thecontact banks pf thereonnectors 200, etc., the extra control conductorofthefirst two private branch exchange trunks 35! and 352 are respectivelyconnected to the control conductors thereof; and likewise, the extracontrol conductor of the party. subscriber line 31!; is connected vtothe control conductor thereof Finally, in the contact banks of theconnectors.

20B,,etc., the party subscriber line 39! terminates on two adjacentrotary contact sets and in the secgnd of the two contact sets the extracontrol and of course, the line conductors and the control conductors ofthe two contact sets are respectively multipled together. Finally in thecontact "banks of the connectors 26!], etc, the positive linethemto-their normal rotary positions. Further a set of switch springsS215 is associated with the wipers noted and is operated when the wipersare driven one step in the counterclockwise direction aw ay from theirnormal rotary positions Finally the. exchange it! comprises a conven;-.tional ringing code interrupter, not shown-hav ing ten, individualringing code; conductors andv a 5PlCK-lipfi0lfldll0t0l 03!] extendingtherefrorn to each of the links, including that illustrated. The

tenindividual ringing code conductors are terminated upon the respectiveten contacts in the; contact bank associated with the -wiper2l! in.

the code switch Z'E'Lincorporated intheconnector 2653;, and the pick-upconductor 03!! Q extends to the contacts 338 of the swit ch throughrelay R33c in the connector 20%.; The ringing code interrupter,not'shown, may be either of the harmonic frequency or of. the codedsplash,

types; whereby the ringing currents applied to;

the ten individual ringing cod e conductors may be either ofcorresponding harmonic; frequencies.

or of corresponding seriesof co ded splashes of short and long durationsIneither. case battery potential in the ringing code. interrupted isappliedto each individnal nodev conductor so that the upper windi g0fthe ringcutoii relay in any connector may be energizedthereover inresponse to an answer upon a called line selected thereby;

allin a conventionalmanner. A better-understanding of arrangement oftheapparatus incorporated in the telephone system will, be iacilitatedfrom a consideration of the extension of variouscalls in the exchangelfil,, j

First assuming ,that a call is initiated at the private subscriber:substation Tlt! in the exchange !0 and isto be extended to a privatesubscriber substation, such for example, as the private subscribersubstatipn Tl 3! in the exchange I 20, when the; call is-initiated atthecalling sub-' scriber substation Tim, the line circuit H0 is controlledover the associated private subscriber nde iqr i peace. t he centra @Q eshtijj,"

"!05 furthe line Hi5; whereby groundpotential in the line.

circuit no is applied to the start conductor C! u extending to thedistributor !-.!2. The distributor operates in response to theapplication of ground potential to the start conductor C! and assigns anidle one of the links, such for example, as that,

illustrated for use at this, time. More particularly, operation of, thefinder N5 of the link illustrated is initiated; whereby the finder !!5operates in order to find the calling private subscriber line !05, theprivate subscriber'line 195,

being marked as a calling line by the application of battery potentialin the line circuit I!) to the control. conductor Cl38 thereofl. Whenthe Q finder I5 finds the calling private subscriber line V wh heir? isar ested mi the connection and calling private subscriber line I05 isseized, ground potential in the finder H5 being applied to the controlconductor CI08 of the private subscriber line I05; whereby the linecircuit H operates to mark the private subscriber line I as busy to theconnectors 200, etc., having access thereto. Also at this time thedistributor H2 is dismissed and the finder H5 is marked as busy thereto.Moreover, a loop circuit is completed between the calling privatesubscriber substation TI 0| and the line relay RI50 in the connector200. This loop circuit extends from ground potential by way of thecontacts I62, the lower winding of the line relay RI50, the contacts 2I4and I46 to the line conductor CI I1; and from battery potential by wayof the upper winding of the line relay RI50 and the contacts 2l2 and I43to the line conductor CH6; the line conductors CH1 and CI I6 areconnected via the finder H5 to the line conductors CI01 and CI06 of theprivate subscriber line I05 and thence to the calling private subscribersubstation TIOI. When this loop circuit is thus completed, the linerelay RI50 operates to complete, at the contacts I5I, a circuit,including the contacts I48, for energizing in series the upper windingof the transfer relay RI60 and the winding of the hold relay RI; wherebythe relays mentioned operate. Also upon operating the line relay RI50completes, at the contacts I5I, a multiple priming circuit, includingthe contacts I48 and the resistor I61, for energizing the verticalmagnet MI66 of the Strowger mechanism 340, thereby rendering thevertical magnet MI66 slightly fast-to-operate when a direct circuittraced hereinafter is completed for energizing it.

Upon operating the transfer relay RI60 completes, at the contacts I6I, apath for connecting ground potential by way of the winding I61 of thedial tone transformer in the loop circuit extending back to the callingprivate subscriber substation TIOI; and interrupts, at the contacts I62,the original path for connecting ground potential in the loop circuitmentioned. Accordingly, at this time dial tone current is returned overthe loop circuit to the calling private subscriber substation TIOIindicating to the subscriber thereat that the directory number of thecalled private subscriber substation TI3I in the exchange 20 may bedialed. Also upon operating the transfer relay RI60 prepares, at thecontacts I64, a direct circuit traced hereinafter for operating thevertical magnet M I66 of the Strowger mechanism 340. Upon operating thehold relay RI10 completes, at the contacts HI a path for applying groundpotential in the connector 200 to the control conductor CI I8 in orderto retain operated the finder H5. Also the hold relay RI10 prepares, atthe contacts I13, a further point in the previously mentioned directcircuit for operating the vertical magnet MI66 of the Strowger mechanism340.

The directory number of the called private subscriber substantially TI3Iin the exchange 20 comprises the prefix digits 0 and 1 followed by anumber of individual digits, and may, for example, be 0II23.Accordingly, the subscriber at the calling private subscriber substationTIOI proceeds to dial the first prefix digit 0; whereby the line relayRI50 follows. Each time the line relay RI50 restores and thenreoperates, it completes and then interrupts, at the contacts I 5|, thepreviously traced circuit for energizing the winding of the hold relayRI10; whereby the latter relayisretainedin its operated position duringimpulsing as it is of the slow-towe lease type. Moreover, the hold relay'RI10 is rendered additionally slow-to-release by virtue of theconnection of the condenser I15 in shunt to the winding thereof; wherebythe condenser I15 is normally charged in multiple with the winding ofthe hold relay RI 10 and is discharged through the winding of the holdrelay RI 10 when the normal circuit for energizing the winding of thehold relay RI10 is interrupted. Also each time the line relay RI50restores and then reoperates, it completes, and then interrupts, at thecontacts I52, a circuit, including the contacts I48, I13 and I63,, forenergizing the lower winding of the transfer relay RI60; whereby thelatter relay is retained in its operated position during impulsing as itis of the slow-to-release type. Also each-time the line relay RI50restores and then reoperates, it completes and then interrupts, at thecontacts I52, a multiple circuit, including the contacts I48, forcharging the condenser H6; whereby the transfer relay RI60 is renderedadditionally slow-to-release. More particularly, the condenser I16 ischarged in multiple with the lower winding of the transfer relay RI60when the circuit mentioned is closed and is discharged through the lowerwinding of the transfer relay R560 when the circuit mentioned is opened.Finally, each time the line relay RI50 restores and then reoperates, itcompletes and then interrupts, at the contacts I52, a multiple directcircuit, including the contacts I43, I13 and I64, for operating thevertical magnet MI66; whereby the wiper carriage of the Strowgermechanism 340 is driven step by step in the vertical direction away fromits normal vertical position. When the wiper carriage of the Strowgermechanism 340 is driven one step in the vertical direction away from itsnormal vertical position, the sets of switch springs SI68 and S246 areoperated. More particularly, the set of switch springs S168 is closed inorder to short-circuit the upper winding of the transfer relay RI60; andto complete a direct circuit, including the contacts I5I and I 48, forenergizing the winding of the hold relay RI10. Also the set of switchsprings S246 is closed in order to prepare a circuit traced hereinafterfor operating the release magnet M2I8 of the Strowger mechanism 340.

At the conclusion of the first prefix digit 0, the line relay RI50 isretained in its operated position and the wiper carriage of the Strowgermechanism 340 occupies its tenth vertical level; whereby the wiper 34I,342, 343 and 344 stand opposite the tenth level in the associatedcontact bank in which the trunk lines I25, etc, are terminated. When thewiper carriage of the Strowger mechanism 340 is thus driven ten steps inthe vertical direction away from its normal vertical position, the setof switch springs S3l6 is operated in order to prepare a circuit tracedhereinafter for energizing the winding of the switch relay R l 40 inmultiple with the lower winding of the test relay R330; and the set ofswitch springs S3I5 is operated in order to prepare a circuit tracedhereinafter for energizing the winding of the rotary step relay R250.Also shortly following the first prefix digit 0, the transfer relay RI60restores, it being of the slow-to-release type, in order to interrupt,at the contacts I 6|, the previously traced path for connecting groundpotential by way of the winding I61 of the dial tone transformer in theloop circuit mentioned; and to recomplete, at the contacts I62, theoriginal path for connecting ground po-w 7 tential in. the ,loop circuitmentioned. Accordingly,.the return of dial tone current over the loop.circuit to the callingprivate subscriber substation TIOI is arrested atthis time. Also upon restoringthe transfer .relayRHifl interrupts, atthe contacts 163, afurther point inthe circuit 'forenergizing the lowerWinding thereof; interrupts, at the contactsl64, a further point in. thedirect circuit forxoperating the vertical magnet M166 of the :Strowgermechanism 340; and prepares, at the contacts 165, a circuit tracedhereinafter for energizing the winding of the seriesirelay R3 in inseries with the rotary magnet M2Lt of the Strowger mechanism 368.

The subscriber at the calling'private subscriber substation Titthen'proceeds to dial the second prefix .digit i whereby the .line.relay R!) again follow. More particularly, the line relay men restoresand then reoperates, interrupting, and then recompleting, at thecontacts 15L the circhit, including the contacts I48 and the set ofswitch springs Si68,:for energizing the winding of the hold relayRl'illywhereby the latter relay is retained in its operated positionduring impulsing, it being of the slow-to-release type. Also the ,linerelay Ri lii completes and then interrupts, at the contacts 552, acircuit, including the-contacts i i-8,173, I65, 265 and 33!), forenergizing the winding of the series relay R359 in series ,with therotary magnet M2l6; of the Strowger mechanism 34%) as well as a multiplepath, also including the contacts did, for energizing the winding of theseries relay Riiiii in series with thewincling of the series slave relayR326; whereby the series relay-RSI'O, the series slave relay R328 andthe rotary magnet M2 It operate. Upon operating the series relay R3liicompletes, at the 'contacts3i2, a point in multiple to the contacts 265for energizing the winding thereof in series with the rotarymagnet M218;interrupts, at the. contacts 314, the original circuit for energizingthe winding of the series relay R3) in series with the winding of theseries slave relay R326; and completes, at the contacts 3l3,-a directcircuit for retaining operated the series slave relay R328. Accordingly,the rotary magnet M2 l6 operates and then restores in order to drive thewiper carriage of the Strowger mechanism S lt one step in the rotarydirection away from its normal rotary position; whereby the Wipers345.1342, 343,.and 3d engage the contactset in the associated contactbank terminating the first trunk line in the group, including the trunkline 4% extending between the. exchanges it and 2t.

Shortly following the second prefix digit i, the series relay R3)restores as it is of the slow-torelease type to interrupt, at thecontacts M3, the circuit for retaining operated the series slave relayR320; whereby the series slave relay R323, being or" the slow-to-releasetype, is retained operated a short-time interval following therestoration of the series relay R35 3. At this time the idleor'busy'condition of the first trunk line in'the group, including thetrunk line I26 is tested; ground potential or battery potential beingpresent upon the control conductor of the first trunk line mentioned inthe eventthe first trunk line is respectively busy or idle. Also theextra control or EC conductor of the first trunk line mentioned isstrapped to the control or C conductor thereof; whereby one of thepotentials mentioned is also applied to the extra control or ECconductor thereof. First assuming that the first trunk line mentioned isbusy, ground=:.potential:appearing upon the control con- 8 ductor,thereof ',-completes .a' circuit, including the control;- wiper;343.,the contact-e335, 323 an 3.31. foroperatingthetest relay R260. UponOperatingthe test relay-R260 completes, at the contacts 1262, a circuit,including the contacts 2|! and 1-3,! i,;;the;set of; switch springsS3l5, the,contactswfi32, :the extra; control wiper 344, and-theextracontrol conductor of the first trunktmentionedahayine gr nd po t threo .i operat et rot y s ep: r lay 3 U n operatin their-otary stenrflayB 56. c mpl tes. at the contacts 25 a hol n circ it ncl d n the con t "ian 2H, for ene izin th wind t eat omplet s t the c n act 252,; analternative, circuit, including the 1 ,contacts I12 and 3 I4, forenergizing the winding oi-the series slave ,relayRSZB;andcompletes, ,atthe contacts 2 52 amultiple circuit, includingthe contacts 112 and 330,for operating the rotary mae. et: 2l e ee di s nc h fi ttrunk line, inthe group, including the .trun kqline 426 is busy, the series slaverelayRBZil isretained in its operated position and the rctarymagnet M256is reoperated. Accordingly, the rotary magnet-M216 reoperates to drivethe wiper carriage of :the .Strowger mechanism 518 .an addi tional stepin .the rotary direction; whereby ,the Wipers ,34 I .342, 35,3 and 13 44 1 disengage the contactset in the associatedcontact bankterminating-the firsttrunk line in the group mentioned and engagethecontactset in the associated contact bank terminating the second trunkline in the group mentioned; whereby the idle or; -b,usy condition ofthesecond trunk line mentionedis tested.

More. particularly, upon operating the rotary n'iagnet M2 I 6 alsointerrupts, at thecontacts :2 7, the holding circuit for retainingoperated the rotary step re1ay'R250; Whereby'the latter relay restoresinterrupting, at the contacts 252, the alternative, holding circuit forenergizing the winding of the series slave relay'R328. andthe multiplecircuit for operating the rotary magnet .,M2IB. Uponrestoring, therotarymagnet MZIG reprepares, at the contacts 2H, ,the circuit for,operatingtherotary step relay R258. Atthis time battery potential isconnectedvia the Winding of the test relay- R269 and-the previouslytraced path to the control wiper d43; whereby. the, idle or busycondition of the second trunkline inthegroupmentioned is tested; thetest relayRZBU reoperating in the event the second trunk line in thegroup mentioned isbusy in the manner previously explained. Accordingly,the connector Ziiiioperates at this timein order to select an idle trunkline in the previously selected group mentioned.

Assuming now that all of the trunk lines in the group mentionedprecedingthe last trunk line I26 therein, are busy at this time, the rotarymagnetM2l6 is operated a corresponding number of times in order to drivethe wiper carriage of the Strowger mechanism'340 a corresponding numberof' steps in. the rotary direction until the wipers 34!, 342, 343 and344 engage the contact set in the associated contact bank terminatingthe last trunk line 126 in the group mentioned. At this time the idle orbusy condition of the last trunk line I26 in the group mentioned istested. First assuming that the last trunk line I26 is also busy, groundpotential appears upon the control conductor'thereof, but no potentialappears upon the extra control conductorthereof since the extracontrol-conductor of the trunk line |26 is'not strapped -to thecontrol-conductor thereof; Accordingly, at-this -time -the previouslytraced circuit for operating the test relay R260 is completed; however,operation of the test relay R260 is without eifect since no potentialappears upon the extra control wiper 344 as noted above. Hence, shortlyfollowing operation of the test relay R260, the series slave relay R320restores as it is of the slow-to-release type. Upon restoring, theseries slave relay R320 completes, at the contacts 324, an alternativeholding circuit, including the contacts 331, 264 and HI, for retainingoperated the test relay R260. Further the series slave relay R320completes, at the contacts 32!, a connection, including the contacts 26Iand 33I and the condensers 3 I 9 and 220, between the busy conductorC3I8 and the line conductor CII1; whereby busy tone current is returnedover the connection to the calling private subscriber substation TIOIindicating to the subscriber thereat that the desired connection may notbe completed at this time due to the busy condition mentioned.Accordingly, the subscriber at the calling private subscriber substationTIOI disconnects in order to eifect the release of the link illustratedin a manner substantially identical to that described hereinafter.

Now assuming that the last trunk line I26 in the group mentioned is idlewhen it is selected by the wipers 34I, 342, 343 and 344 of the Strowgermechanism 340, battery potential appearing upon the control conductorthereof completes a path substantially identical to that previouslytraced for short-circuiting the winding of the test relay R260 wherebythe latter relay is not operated at this time. Accordingly, shortlythereafter, when the series slave relay R320 restores, it interrupts, atthe contacts 323, the path for short-circuiting the winding of the testrelay R260; and completes, at the contacts 322, a circuit, including thecontacts 336, 263 and Ill and the control wiper 343, for energizing theupper winding of the switch-through relay R330; whereby the latter relayoperates shortly thereafter, it being of the slow-to-operate type. Uponoperating the switch-through relay R330 completes, at the contacts 334,a holding circuit, including the contacts I12, for energizing the lowerwinding thereof; and completes, at the contacts 335, a direct path,including the contacts I12, for applying ground potential to the controlwiper 343. Also the switch-through relay R330 completes, at the contacts334, a multiple circuit, including the contacts I12 and the set ofswitch springs S3I6, for operating the switch relay RI40. Upon operatingthe switch relay RI40 completes, at the contacts I42 and I 45, a directconnection between the line conductors CI I6 and CI I1 and the lineWipers 34I and 342 and consequently a direct loop circuit between thecalling private subscriber substation 'IIOI and the line relay, notshown, in the trunk circuit I25 terminating the trunk line I 26. Theloop circuit extending from the private subscriber substation 'I'IIlI tothe trunk circuit I25 includes the private subscriber line I05, the linecircuit H and the finder I I5, the connector 200 and the trunk line I26.When this loop circuit is completed, the trunk circuit I 25 operates toreturn ground potential over the control conductor of the trunk line I26thereby to complete an alternative holding circuit, including thecontrol Wiper 343 and the contacts 335 and 334, for energizing the lowerwinding of the switch-through relay R330 and a multiple holding circuit,also including the set of switch springs S3I6, for energizing thewinding 0f the switch relay RI40. i

Also upon operating the switch relay RI40 interrupts, at the contactsI43 and I46, the original loop circuit extending to the upper and lowerwindings of the line relay RI50 in order to cause the latter relay torestore. Further the switch relay RI40 completes, at the contacts I41, amultiple path for applying ground potential to the control conductorCH8; and interrupts, at the contacts I48, the circuit for energizing thewinding of the hold relay RI10 in order to cause the latter relay torestore shortly thereafter, it being of the slow-to-release type.Accordingly, at this time, the connector 200 is switched through andonly the switch relay RI40 and the switch-through relay R330 thereinoccupy their operated positions. Moreover, when the trunk circuit I25 isthus seized, the trunk circuit I21 in the exchange 20 is governed overthe associated trunk line I26; whereby the automatic switch train I28 inthe exchange 20 is operatively associated with the trunk circuit i21.

At this time the subscriber at the calling private subscriber substationTIOI proceeds to dial the three digits I, 2 and 3; whereby the digitsmentioned are transmitted over the loop circuit to the trunk circuit I25; whereupon the trunk circuit I25 repeats the three digits mentionedover the trunk line I26 to the trunk circuit I21; and the trunk circuitI21 repeats the three digits mentioned to the automatic switch train I28. The automatic switch train I28 responds to the three digits I, 2 and3 to select the private subscriber line I29 extending to the calledprivate subscriber substation TI3I in the exchange 20; whereupon theidle or busy condition thereof, as marked by the associated line circuitI30, is tested in the automatic switch train I 28. Assuming that thecalled private subscriber substation TI3I is idle at this time, theautomatic switch train I28 operates to project ringing current theretoover the associated private subscriber line I26; and when the call isanswered at the called private subscriber substation TI3I, the automaticswitch train I28 switches through, thereby completing an estab lishedconnection between the calling private subscriber substation TIOI in theexchange I0 and the called private subscriber substation TI3I in theexchange 20.

At the conclusion'of this established connection when the subscriber atthe calling private subscriber substation TIOI in the exchange I0disconnects, the loop circuit extending therefrom to the trunk circuitI25 is interrupted; whereby the trunk circuit I25 operates in order toremove the application of ground potential from the control conductor ofthe trunk line I26, thereby to interrupt the holding circuitsforenergizing the lower winding of the switch through relay R330 and thewinding of the switch relay RI40 causing the relays mentioned torestore. Upon restoring the switch relay RI40 interrupts, at thecontacts I41, the path for applying ground potential to the controlconductor CI I8, thereby to eiiect the release of the finder H5;whereupon ground potentialis removed from the control conductor CI08 ofthe private subscriber line I05. At this time battery potential in theline circuit I I0 individual to the private subscriber line I05 isreturned upon the control conductor thereof, thereby marking the privatesubscriber line I05 as idle to the connectors 200, etc., having accessthereto. Also upon restoring the switch relay RI40 completes, at thecontacts I40, a circuit, including mthe CIII extending to the" finderH5.

11 contacts I52. and? H6 and theesetaof: switch springs S246 foroperating" thereleaseqmagnet MZ-IB' -whereby the .wiper carriage -of theStrowger mechanism 340 is released and: returned .to' its normalrotaryand vertical posi tions; When'the' wiper carriage of the Strowgermechanism 340 is thus released, the sets of switch springs SIES,S246jS3I5 and S3%% are operated. More particularly, the set of switchsprings :SI 68 is operated" to open the path for short-circulting theupper winding of the transfer relay*RI60;' and the set" of switchsprings $24648 operated-to open thecircuit for operating 'the releasemagnet M2 I8. The set'of switch springs-SHE is operatediiin order toopen a fur-- ther point in-the-' circuit for operating the rotary steprelay R250; and" the set of switch springs s3I6' is operated in order toopen 'a further-point' in the circuit for operating the switch IelayRMIl'. Further the-switch rela RIM) recompletes, at the contacts I43 andl46-gthe normal connections from battery and ground potential viatheupper andlower windings'of the line rela y R150 to the lineconductors CI I5 and Moreover, when th'efinder I I5 is thus released, itis marked as idle"'to the" distributor I I 2 for reassignment thereby:At this timethe" connector 200 is releasedandthe trunlc of circuit I25operates in order to return battery potential to the control conductorof the trunkllne-IZB; whereby the trunk line I2Bis-marked as idle totheconnector-s 100; etbl', having-access thereto.- Furthermore? thetrunk circuit I25" controls the trunk circuit I2=1 inthe exchange 20'over the trunk line I 26; wherebythe trunk'circuit I21and'cons'equently the'automatic switch train I28 in the exchange 20 arereleased. Whenthe automatic switchtrain I28 isthus-released, thelinecircuit. I30 individually associated with'the private subscriber lineI29 operates in orderagain to apply battery potential to the controlconduc torof 'the privatesubscriber linel29, assuming that thesubscriber atthe private subscriber substation vT I 31 has disconnectedat this time; whereby the 'private subscriber-iine429 is again marked asidle to the automatic switch "train I28. 7 I At this" time: theestablished "connection be tween the callin private subscribersubstationTlll l' in"the' exchange 1'8 and th'e called private subscribersubstation T I 31 in "the exchange 2F) is released and' all of theapparatusinvolved therein is" completely released and" available forfurther use Now assuming'th'at'a call is to be ext'ended fromthe-private subscriber substationTHJI to the" P. B. X 350 in theexchangeI0, the call is .firs'tiinitiatedatmthe calling private subscribersubstation TIUI'; whereby the distributor H2 may assign the linkillustrated-for use; whereby the'finder H5 finds the. privatesubscriber-line lllfi 'exten'ding to thecalli-ng private subscribersubstation TI ll I; iandr the: line rrelay T R I 5!! '1 in the connector2'80 is operated; all: in themanner previously explained; .lUp'onoperating the line relay 'R lilfljeflfects operation of the transferrelay-RISE and the hold relay RN 0; the'transfer relay RI 3Q bringingabout the return 'of 1 dial ton'ewover the loop circuitto the*callingprivate'subscriber substation TI (II in the manner:previously-explained, At this time'the subscriber: at the calling privatesubscribersubstation 'IIOI' dials-1 the directory number of the P. B; X350,- which number may be=911. A v

When the first digit 9 is dialed; the line relay l2 RIEDfollowsretaining operated the transfers-re lay-R'Ifili and'thetholdrelayRI!!! and effecting operation of the verticalmagnet MI= in the mannerpreviously; explained. 'At the conclusion of the first digits, thewipercarriage of the Strowger mechanism'BMl occupies its ninth'verticallevel; whereby thS'WiPGIS SM, 362, 343 and 344 stand opposite'ztheninthlevel in the associated contact bank in which the P. B. X trunks 35I,352 and 353 are terminated. When the wiper carriage of the Strowgermechanism 348 is driven one stepin the vertical direction awayfrom itsnormalvertical position, the setsof switch springs SI cs and'szds areoperated as'previously explained. Also whenthewiper carriage of theStrowger mechanism .340 is driven nine stepswin the vertical directionaway from-its normallver tical position, the sets 'of switchsprings S3l5and S246 are operated. Moreparticularly, .the'

set of switch springs 53w is operated into en gag'emen'tin ordertoprepare the previously traced circuit for operating the: rotary step re-Iay RZEll'; and the. set of switch springs SMSs is operated intodisengagement in order to inter rupt a further point in a circuit tracedherein after for operating the ring reverse relay'RZBU. At theconclusion of 'the first digit 5, thelline relay Rl5fl is retained inits operated position in order to cause the transfer relay RIG!) torestore shortly thereafter, the latter relay being of theslow-to-release type;

At this time the subscriber at 'thecalling private subscriber substationTI EII' dials the second digit I; whereby the line relay RIEQfollows=re-'- peating; at the contacts I52, in order'to'r-effectoperation of the seriesrelay R3I0 and the series slave relay R329 andthe rotary magnet M216; More particularly, the rotary magnetMZIfi' opcrates and then restores in order to drive the wiper carriage of theStroWger mechanism 340 one step in the rotary direction away'from its 7normal rotary position; whereby 'the-wipers3M.

342, 343 and-.344 engage the contact set in the associated contact bankterminating the first P. B. X trunk 35!. At the'con'clusion of theseconddigit I, the linerelayRIEli is retained inits operated position inorder to cause the series relay R3! to restore shortly thereafter.Atthis time the test relay R26iitests theidle or" busy condition of thefirst P; B. X trunk 35L Specifically, assuming that the first P; B. Xtrunk '35I is busy at'this time, ground potential in the associated linecircuit 354 appears upon the control conductor thereof and consequentlyupon the connected extra control-conductor thereof. The application ofground potential upon the control conductor of the first P. B. X trunk35I completes the previously traced circuit, including the con operatingthe rotary magnet M2IE. Upon operating the rotary magnet MZI Sinterrupts, at the contacts 2", the 'circuitfor retaining: operated therotary step relay R250; whereby the latter relay interrupts, at the"contacts 252,'the alterna 'tive holding circuit forenergizingthewinding of the series slave relay R320 and the multiple circuit foroperating the rotary magnet M2I0. Accordingly, the rotary magnet M2I6operates and then restores in order to drive the wipers 34l, 342, 343and 344 into engagement with the contact set in the associated contactbank terminating the second P. B. X trunk 352; whereby the idle or busycondition of the second P. B. X trunk 352 is tested by the test relayR260. Of course, the second F. B. X trunk 352 is selected in the eventit is idle and on the other hand, in the event it is busy, the rotarymagnet M2IE is reoperated, in the manner previously explained, to drivethe wiper carriage of the Strowger mechanism 340 an additional step inthe rotary direction; whereby the wipers 34I, 342, 343 and 344 selectthe contact set in the associated contact bank terminating the third P.B. X trunk 353. Assuming that the second P. B. X trunk 352 is also busy,the rotary magnet M2I6 is reoperated as explained above, whereby thethird P. B. X trunk 353 is selected and tested.

First assuming that the third P. B. X trunk 353 is busy at this time,ground potential appearing upon the control conductor thereof completesthe previously traced circuit for operating the test relay R260; howeversince the control conductor of the third P. B. X trunk 353 is notstrapped to the extra control conductor thereof, the previously tracedcircuit for operating the rotary step relay R250 is not recompleted.Accordingly, the rotary magnet M2"; is not reoperated; and shortlythereafter, the series slave relay R320 restores, completing, at thecontacts 324, the previously traced holding circuit for retainingoperated the test relay R260; and completing at the contacts 32I, thepreviously traced path for returning busy tone current over the loopcircuit to the calling private subscriber substation 'IIOI in order toindicate to the subscriber thereat that the desired connection may notbe had at this 4 time by virtue of the busy condition noted. Thesubscriber at the calling private subscriber substation TIOI thendisconnects in order to efiect the release of the apparatus in a mannersubstantially identical to that previously explained.

Now assuming that the third P. B. X trunk 353 is idle when it isselected by the wipers 34I, 342, 343 and 344 of the Strowger mechanism340, battery potential appearing upon the control conductor thereofcompletes the previously mentioned path for short-circuiting the windingof the test relay R260 in order to prevent operation of the latterrelay. Shortly thereafter, the series slave relay R320, being of theslow-to-release type, restores to complete, at the contacts 322, thepreviously traced circuit for energizing the upper winding of theswitch-through relay R330; whereby the latter relay operates shortlythereafter to complete, at the contacts 334, the previously tracedholding circuit for energizing the lower winding thereof, theswitch-through relay being of the sloW-to-operate type. Also theswitchthrough relay R330 completes, at the contacts 335, the previouslytraced path, including the contacts I12, for applying ground potentialto the control wiper 343 and consequently to the control conductor ofthe third P. B. X trunk 353 extending to the associated line circuit 356in order to mark the third P. B. X trunk 353 as busy to the otherconnectors having access thereto. Also the switch-through relay R330interrupts, at the contacts 330, a further point in the previouslytraced circuit for operating the rotary magnet M2I3 in order positivelyto prevent further operation of the Strowger mechanism 340 in the rotarydirection at this time; and prepares, at the contacts 339', a circuittraced hereinafter for operating the rotary magnet M213 of the codeswitch 210.

When the subscriber at the calling private subscriber substation 'IIOIdials the third digit I, the line relay RI50 follows. More particularly,the line relay RI50 restores and then reoperates completing and theninterrupting, at the contacts I52, a circuit, including the contactsI48, I13, I35, 266, and 3I4, for energizing the winding of the seriesrelay R3 I 0 in series with the winding of the series slave relay R320in order to cause the relays mentioned to reoperate. Also the line relayRI 50 completes and then interrupts, at the contacts 652, a multiplecircuit, including the contacts I48, I13, I65, 266 and 339, forenergizing the winding of the series relay R3 I 0 in series with therotary magnet M213; whereby the rotary magnet M213 is operated in orderto drive the wipers 21I and 212 of the code switch 210 one step in thecounterclockwise direction away from their normal rotary positions. Whenthe wipers noted 0! the code switch 210 are thus driven one step in thecounterclockwise direction away from their normal rotary positions, theset of switch springs S215 is operated for a purpose more fullyexplained hereinafter. When the wiper 21I of the code switch 210 isdriven to engage the first contact in the associated contact bank, thefirst ringing code conductor extending to the associated ringing codeinterrupter, not shown, is selected for a purpose more fully explainedhereinafter.

At the conclusion of the third digit I, the line relay RI50 is retainedin its operated position, and shortly thereafter, the series relay R3I0, being of the slow-to-rclease type restores; whereby the series siaverelay R320 being of the slow-torelease type, restores after anadditional short time interval. Upon restoring the series slave relaR320 completes, at the contacts 325, a direct circuit, including the setof switch springs S215, for operating the test relay R260. Uponoperating the test relay R2 60 completes, at the contacts 235, aconnection, including the contacts 338 and 224, between the pick-upconductor C3 I1 extending to the associated ringing code interrupter,not shown, and battery potential via the winding of the pick-up relayR220. At the beginning of a ringing cycle of the ringing codeinterrupter, not shown, ground potential is applied to the pick-upconductor C3 I1; whereby the winding of the pick-up relay R220 isenergized causing the latter relay to operate. Upon operating thepick-up relay R220 completes, at the contacts 223, a holding circuit,including the contacts I12, for energizing the winding thereof; andcompletes, at the contacts 22! and 222, a path for projecting ringingcurrent from the first ringing code conductor over the selected third P.B. X trunk 353. More particularly, ground potential is connected via thecontacts I12, the contacts 243, 233, 222 and I44- and the line wiper 342to the positive line conductor of the third P. B. X trunk 353; and thefirst ringing code conductor is connected via the wiper 21I of the codeswitch 210 and the engaged first contact in the associated contact bankand the upper winding of the ring cut-off relay R230, the contacts-24L23!, 22I and MI and the line wiper 34! to the negative line condoctor ofthe third P. B. X trunk 353. Accordingly, ringing current from theselected first ringing code conductor is projected over the lineconductors of the selected third P. B. X trunk 353 in order to operatethe signal drop or ringer at the P. B. X 350 in a conventional mannerindicating to the attendant thereat that a call is waiting toberansweredon the; third 1. B; 'X1trunk;.353. Also portionlof: thisringing, current. isreturned aszring-back'tonexcurrent .to the callingprivate subscriber..-substation,T l indicating to thesubescribenthereatthat the callediPL B. X350is being rungs-at" this time.vMore particularly, the negativelline wiper. 3Mincluded inthe ringingcircuit above tracedisxconnected via the contacts Ml, the condensers 22?and225and the contacts I43 to'the :line conductor-Cl I6; and thepositive line wiper: 3142 included in the ringing circuit above tracedisconnected viathe contacts I44, and the condensers122'82 and 226. to theline conductor CH7; and the line conductors CH6 and CH1 being includedin the previously traced loop circriituextending-baclr tozthecalling-private subscriber; substation TI 0 If.

When-the attendant at the P. B. X 3% answers the callz-by connectingv tothe line conductors of the third P. B. X trunk 3553, a low resistancecircuitsridentical to that previously traced, is con pletedriorenergizingthe upper winding of the ringacuteoff relay Rfiflin order tocause the latterirelayto operate shortly thereafter, it being of thecombination slcw to-bperate and slow-torelease type. Upon operatingthering cut-on lav R239 completes, at the contacts 236, a holingcircuit;lincluding the contacts H2, for energizing the-lower windingthereof interruptsvat the contacts ilsl -nand 233, the path forprojecting ringing currentsover the'line conductorsof the selectecLthirdP. BiXtrunk i 53 and the path for returning ring-back tone current tothe calling private subscriber substation T ill pletes', at the-contacts232, 23,and 235, a loop circuit between the upper and lower windings ofthe back-bridge relay R2lll and. the called P. B. X 359; Moreparticularly, ground potential is connected by way of the contacts 235,the lower windingof the back-bridge relay REM the contacts 234, 222, andM4, and the linewiper 352 to the positive line conductor of the third P.B. trunk 353; and battery potential is connected by wayofthe'upper'winding of the back-bridge relay- RZ'E'B, theconta-cts 2'32,221 and H12, and the linewiper S ll to the negative line conductor ofthethirdP. B. X 353. A ccrdingly, the upper and lower windings or".theback-bridge relay 132W are energized in series via the above tracedcircuit; whereby the'latter relay operates.

Upon-- operating the back-bridge relay R225 reverses, at thecontactsEll, 2E2, 293, and 2M, thepolarity of theloo'p circuit extending betweenthecalling private subscriber substation Till! and the upper and lowerwindings of the line relay RlSil; which reversal of polarity over theloop;circuit mentioned may be employed in the line circuit Hi3individual to the private subscriber line 185' extending to the callingprivate subscriber substationTllH for metering or other control.purposes in a conventional manner. Also at this time, the loop circuitextending between the calling private subscriber substation Tlili andthe upper and'lower windings of the line re:- lay Rh'ld and the loopcircuit extending between the called P. B. X 359 and the upper and lowerwindings of the backebridge relay RZlt are operatively interconnected bythe condensers 225 and 2.25; whereby an established connection iscompleted between the calling private subscriber substationiTllll.andthe called P. B. X 35!). Fur- .ther, upon operating, the back-bridgerelay R259 completes, at the contacts 2l5, a multiple path iorapplyingground potentialto the control conand como 16 ductor Cl l8 in order: toretain thefinder 1=l l5-'-in its operated position.

t the conclusion of the established connection, when the attendant atthe P. B. X 350 or a subscriber at a substation therein disconnects, theloop circuit extending therefrom to the backbridge relay R2 it isinterrupted, causing the lat- .scriber substation Tlil-I disconnects,the loop circuit, extending to the line relay RIM) is inter: rupted,causing the latter relay-to restore. Upon restoring the-line relayRlfifi' interrupts, at the contacts lfil, the-circuit for energizing thewinding' or; the hold relay; Rlli'l; whereby the latterrelayrrestoresshortly thereafter, it being or" the slow-to-release type.Uponrestoring the hold relay 1115,79 interrupts; at the contacts Hi, thepathfor, applying; ground potential to the con,- trol conductor Cl i8;whereby the'finder H5'is released; bringing about the release of theline circuit, H0 inorder. to cause the private subscriber line lilliagain to be marked as idle to the connectors 2%, etc., having accessthereto; Also thehold relay Rllll completes, at the contacts fi l-,1 thepreviously traced circuit for operating the release. magnet M2l8;whereby the wiper carriageof the-Strowger mechanism 3% is released andreturned to its normal rotary and vertical positions; Also the holdrelay Rl'lll completes, atithe'contacts lit, a multiple'circuit,including the'contacts I 28, I52, and 267; for operating the release.magnet M214 of the code switch 210; whereby the wipers 2H and 2'52thereof are released anol. returnedto their normal rotary positions;Further upon restoring the hold relay Ri'lil'interrupts, at the contacts572, theholding circuits for energizing in multiple the winding of thepick-up relay R229, the lower winding of the ring cut-off relay R230 andthe lower winding of the switch-through relay R330; whereby the pickuprelay R220 and the switch-through relay R330 restore immediately andthe-ring cut-off relay R230 restores shortly thereafter, it being of thecombination slow-to-operate and slow-to-release type:

When the Strowger mechanism 346 is thus released, the sets of switchsprings Sl68, S246,

S3I5 and 8M8 are operated. More particularly,

springs SZ'lEv is operated to interrupt the: circuit thereto. At thistime the established connectionbetween the calling private subscribersubstation TIOI and the P. B. X 350 is released and all of the apparatusinvolved therein is completely released and available for further-use.

Now assuming that a call is to be extende from the calling privatesubscriber substation TI to the party subscriber substation 36IAconnected to the party subscriber line 33| in the exchange I0, the callis first initiated at the calling private subscriber substation TIOI;whereby the distributor I I2 may assign the link illustrated for use;whereby the finder H5 finds the private subscriber line I05 extending tothe calling private subscriber substation TI 0% ;and the line relay R I50 in the connector 200 is operated; all in the manner previouslyexplained. Upon operating the line relay RI50 effects operation of thetransfer relay R100 and the hold relay RI; the transfer relay RIBUbringing about the return of dial tone over the loop circuit to thecalling private subscriber substation TI 0! in the manner previouslyexplained. At this time the subscriber at the calling private subscribersubstation TIOI dials the directory number of the called partysubscriber substation 36IA, which. number may be 611.

When the first digit 0 is dialed the line relay RI50 follows retainingoperated the transfer relay RI 00 and the hold relay RIM and effectingoperation of the vertical magnet MISIS in the manner previouslyexplained. At the conclusion of the first digit 8, the wiper carriage ofthe Strowger mechanism 340 occupies its sixth vertical level; wherebythe wipers 34!, 342, 343 and 344 stand opposite the sixth level in theassociated contact bank in which the party subscriber line 30I isterminated. When the wiper carriage of the Strowger mechanism 340 isdriven one step in the vertical direction away from itsnormal verticalposition, the sets of switch springs SIGB and S240 are operated aspreviously explained. At the conclusion of the first digit 6, the linerelay Rl50 is retained in its operated position in order to cause thetransfer relay RISE) to restore shortly thereafter, the latter relaybeing of the slowto-release type.

, At this time, the subscriber at the calling private subscribersubstation Ti-0| dials the second digit l; whereby the line relay R150follows repeating at the contacts I52 in order to effect operation ofthe series relay R3|0 and the series slave relay R320 and the rotarymagnet M2I6. More particularly, the rotary magnet M2I0 operates and thenrestores in order to drive the wiper' carriage of the Strowger mechanism340 one step in the rotary direction away from its normal rotaryposition; whereby the wipers 34I, 342, 343 and 344 engage the contactset in the associated contact bank terminating the party subscriber line301 to which the party subscriber substations 36IA, etc., are connected.At the conclusion of the second digit I, the line relay RI50 is retainedin itsoperated position in order to cause the series relay R3l0 torestore shortly thereafter. 'At this time the test relay R200 tests theidle or busy condition of the party subscriber line 36I. First assumingthat the party subscriber line 36! is busy at this time ground potentialis applied to the controlconductor thereof in the associated linecircuit 352, thereby to complete the previously traced circuit includingthe control wiper 343 for operating the test relay R260. Upon operatingthe test relay R260 prepares, at the contacts 264, the holding circuitfor energizing the winding thereof. Shortly following the restoration ofthe series relay R3I0, the series slave relay R320 restores as it is ofthe slow-to-release type. Upon restoring the series slave relay R320completes, at

the contacts 324, the previously traced holding circuit for energizingthe winding of the testrelay R250; and interrupts, at the contacts 323,the previously traced original operating circuit for the test relayR200. Further the series slave relay R320 completes, at the contacts32!, the previously traced path for returning busy tone over the loopcircuit extending to the calling private subscriber substation TI 0| inorder to indicate to the subscriber thereat that the desired connectionmay not be had at this time due to the busy line circuit 362 appearsupon the control conductor thereof, thereby to complete a path identicalto that previously traced for, short-circuiting the winding of the testrelay R260 preventing operation of the latter relay at this time.Subsequently, when the series slave relay R320 restores, it interrupts,at the contacts 323, the path forshortcircuiting the winding of the testrelay R260; and completes, at the contacts 322, the previously tracedcircuit, including the control wiper 343, for energizing the upperwinding of the switchthrough relay R330; whereby the latter relayoperates shortly thereafter, it being of the slow-tooperate type. Uponoperating the switchthrough relay R330 completes, at the contacts 334,the previously traced holding circuit for ener: gizing the lower windingthereof; completes, at the contacts 335, the previously traced path forapplying direct ground potential to the control: wiper 343 in order tomark the party subscriber line 36I as busy to the other connectorshaving access thereto; and prepares, at the contacts 339, the circuitfor operating the rotary magnet M213 of the code switch 210.

When the subscriber at the calling private sub scriber substation TIOIdials the third digit I, the

line relay RI50 follows repeating, at the contacts I52, in order toeffect operation of the series relay R3I0 and the series slave relayR320 and the rotary magnet M213 of the code switch 210. Moreparticularly, the rotary magnet M213 is operated and restored; wherebythe wipers noted of the code switch 210 are driven one step in thecounterclockwise direction away from their normal rotary. positions; andthe set of switch springs S215 is operated. When the wiper 21I of thecode switch 210 is driven to engage the first contact in the associatedcontact bank the first ringing code conductor extending to theassociated ringing code interrupter, not shown, is selected.

At the conclusion of the third digit I, the line relay RI50 is retainedin its operated position and shortly thereafter, the series relay R3I0,being of the slow-to-release type; restores; whereby the series slaverelay R320, being of the slowto-release type, restores after anadditional short time interval efiecting operation of the test relayR260 in the manner previously explained. Upon operating the test relayR236 prepares, at the contacts 265, the circuit to the winding of thepick-up relay R220; whereby the pick-up relay R223 is operated via thepick-up conductor 03H at the beginning of the next ringing cycle of theringing code interruptennot shown. Upon operating the pick-up: relayR220 completes, at the contacts 223, the previously traced holdingcircuit for energizing the winding thereof; and com pletes, at thecontacts 22I and222, the previously traced path for projecting ringingcurrent from the first ringing code conductor over the party subscriberline 361; and for returning ring back tone current over the loop circuitextending to "the calling private subscriber substation TIiII partysubscriber substation 36IA, 36iB, etc., is

operated, but only the ringer at the called party subscriber substation3$IA is operated'in accordance with the assigned code.

etc., bring about corresponding settings of the code switch 210 in orderto cause selection of the corresponding second, third, etc., ringingcode.

conductorsextending to the'ringing code interrupter, not shown.

ductors, in turn, bring about eorresponding oper. ation of the ringersat the respective called party subscriber substations 3BIB, 36 IC, etc.,in a mane ner similar to that described above.

Now assuming that a call is to be extended from the calling privatesubscriber substation TIM to one of the called party subscribersubstations 38IA, 38IB, etc., connected to the party P subscriber line38I in the exchange III, the subscriber at the calling privatesubscriber substation TIEH first initiates thecall' and then dials thedirectory number of the called party subscriber substation 38IA, 38IB,etc.; which num-.

. bers are respectively 8| I, 8I2, etc. Again assum ing that'the linkillustrated is assigned'by the In any case the subscriber at the calledparty subscriber substation 36 IA is signalled; and when the subscriberthereat answers the call, the previously traced circuit for energizingthe upper winding of the ring cut-off relay R230 is completed, causingthe latter relay to operate shortly thereafter, it being of thecombination slow-tooperate and slow-to-release type. Upon operating thering cut-off relay R230 completes, at the contacts 236, the previouslytraced holding circuit for energizing the lower winding thereof inlterrupts, at the contacts 23I and 233, the path for projecting ringingcurrent over the party subscriber line 361 and the path for returningring-back tone current to the calling private subscriber substationTIOI; and completes, at the contacts 232, 234, and 235, the previouslytraced loop circuit from the called party subscriber substation 36IA tothe upper and lower windings of the back-bridge relay R2 I0 causing thelatter relay. to operate. Upon operating the back-bridge relay R2!reverses, at thecontacts 2| I, 2I'2, 2I3 and2I4, the polarity of theloop circuit extending back to the calling private subscriber substationTIOI; 'At this time an established connection is completed between thecalling private subscriber substation'TIOI and the called partysubscriber substation 3BIA. The release or this established connectionis brought about when the subscriber at thecalled party subscribersubstation 36IA and the subscriber at the calling private subscribersubstation TIIII both disconect; all in the manner.previously'explained.

In view of the foregoing it will be understood that the subscriber atthe calling private subscribersubstation TIIlI may extend acallto anyone of the other party subscriber'substations 36 IB, 36IC, etc., in asubstantially identical man- 7 ner by dialing the corresponding directlynum-' bers 6I2, BI3, etc. When these directory num-l bers arethusdialed, the first two digits 6 and I bring about selection by the wipercarriage of the Strowger-meohanism 3400f the party subscriber l e 3 1;whereas-t e. r -di ts: 31,

iii

distributor I I2 for use at this time, the connector 3 200 responds tothe number 8H, 8I2, etc., in the manner previously explained. Moreparticularly, the first two digits 8 and I bring about operation of thewiper carriage of the Strowger mechanism 3% to select the partysubscriber line 38I to which the party subscriber substations 38IA, 3MB,etc., are connected. The third digit I, 2, etc., is registered in thecode switch 210 in order to cause selection of the corresponding first,second, etc., ringing code conductor extending to the ringing codeinterrupter, not shown. The ringing code on the corresponding first,second, etc., ringing conductor, in turn, brings about correspondingoperation of the ringer at the corresponding called party subscribersubstation 38IA, 38IB, etc., in a manner similar to that-describedabove. In this connection, it is pointed.

out that the ringing current that is projected over the negative linewiper 34! and the negative line conductor of the party subscriber line38| includes the section of earth between ground potential in theexchange I0 and ground potential at the called party subscribersubstation 38IA, 38IB, etc., sincelthe negative line conductor of theparty subscriber line 38I is connected through the ringer at the calledone of the party subscriber substations 38I', 38IB, etc., directly toground potential thereat. Similarly, when an established connection isultimately completed to the called party subscriber substation 38 IA, 38IB,

substation apparatus at the called party sub scriber substations SBIA,38IB, etc. The subsequent release of this established connection and theapparatus involved therein is identical to that previously described.

Now assuming that a call is to be extended 7 from the calling privatesubscriber substation TIOI to one of the called subscriber substations31 IA, 3'iIB, etc., connected to the party subscriber line 3H in theexchange ID; the subscriber at the calling private subscriber substationTIDI first initiates the call and then dials the directory number of thecalled party subscriber substation 315A, 3IIB, etc., which numbers arerespectively II I, I I 2, etc. Again assuming that the link illustratedis assigned by the distributor H2 for use at this time, the connector200 responds to the numbers II I, 'II2, etc., in the manner previouslyThe ringing codes on the corresponding second, third, etc., ringingconexplained. More particularly, the first two digits 1 and I bringabout operation of the wiper carriage of the Strowger mechanism 340 toselect the party subscriber line 31! to which the party subscribersubstations 3'HA, 3HB, etc., are connected. The third digit l, 2, etc.,is registered in the code switch 210 in order to cause selection of thecorresponding first, second, etc., ringing code conductor extending tothe ringing code interrupter, not shown.

, In the event the present call is to be extended,

to one of the first five party subscriber substations 3HA, 3HB, 3'HC,3'HD and 3HE connected to the party subscriber line 31!, thecorresponding third digit 1 2, 3, 4 or 5 is registered in the codeswitch 210, and ringing over the negative line wiper 3 in the connector200'takes place in.

precisely the same manner as that previously explained; whereby theringer at the called private subscriber substation 3'IIA, 3'HB, etc.,connected between the negative line conductor of the party subscriberline 31! and ground potential thereat, is operated directly over thenegative line conductor of the party subscriber line 31 I. For example,this ringing circuit may extend from one terminal of the ringing codeinterrupter, not, shown, via the first ringing code conductor, the wiper2' of the code switch 210, and the engaged first contact in theassociated contact bank, the upper winding of the ring cut-off relayR230, the contacts 24!, 231, 221, and MI, the negative line wiper 3, thenegative. line conductor of the party subscriber line 3'", and theringer at the party subscriber substation 3HA to ground potential;thence via the section of earth between ground potential at the calledparty subscriber substation 3HA to ground potential in the exchange l0to which the other terminal of the the loop, circuit between the calledparty sub-..

scriber substation 31|Aand the upper end lower windings of thebackbridge relay R2 l 0; all in the manner previously explained.

On the other handin the event the presentcall is to be extended to oneof the second five party subscriber substations 3'IIF, 3HG, 37 l H, 3HI

and 3HJ connected to the party subscriberline 3, the corresponding thirddigit 6, 7, 8, 9, or 0 is registered in the code switch 210. Accordinglyin this special event when the switch-through relay R330 operates, theparty subscriber line 31! having previously been tested as idle by thetest relay R260, it also completes, at the contacts 333, a circuit foroperating the ring reverse relay R240. This circuit extends from thegrounded control conductor of the party subscriber line 3' via the strapto the extra control conductor thereof and thence via the extra controlwiper 344, the contacts 333 and the set of switch springs S248 to thewiper 212 of the code switch 210. At this time the wiper 212 of the codeswitch engages one of thesixth to the tenth contacts in the associatedcontact bank completing the circuit through the winding of the ringreverse relay R240 to battery potential. 'Upbn operating the ringreverserelay R240 reverses,;ati:the.contacts 241,242; 243and 2.44, theconnectionsbetween :the wiper 2' act,

the code switch 210 and ground potential at the contacts I12 and theline wipers 3 and 342. More specifically, at this time the wiper 2' ofthe code'switch 210 is connected via the upper winding of the ringcut-off relay R230, the con tacts 242, 233,222, and I44, to the positiveline wiper 342; and ground potential at the contacts I12 is connectedvia the contacts 244, 23l, 22| and 14! to the negative line wiper 34!.Accordingly, ringing current is projected over the positive lineconductor of the party subscriber line 3; whereby the ringer at thecalled party subscriber substation 3HF, 311G, etc., connected betweenthe positive line conductor of the party subscriber line 31! and groundpotential thereat is operated directly over the positive line conductorof the party subscriber line 3'". For example, the ringing circuit mayextend from one terminal of the ringing code interrupter, not shown, viathe sixth ringing code conductor, the

wiper 2' of the code switch 210 and the engagedv sixth contact in theassociated contact bank, the upper winding of the ring cut-oil relayR230, the contacts 242, 233, 222 and Hi, the positive line wiper 342,the positive line conductor of the party subscriber line 31! and theringer at the party subscriber substation 3HF to ground potential;thence via the section of earth between ground potential at the calledparty subscriber substation 3HF to ground potential in the exchange 10to which the other terminal of the ringing code interrupter, not shown,is connected. Subsequently, when the subscriber at the called partysubscriber substation 31 IF answers the call, a circuit substantiallyidentical to that previously traced and including the upper winding ofthe ring cut-off relay R230 is completed; whereby the latter relayoperates in order to arrest the projection of ringing current over theparty subscriber line 311 and the return of ring-back tone current tothe calling private subscriber substation T10! and to complete the loopcircuit between the called party subscriber substation 31 IF- and theupper and lower windings of the backbridge relay R2I0; all inthe mannerpreviously explained. The subsequent release of this establishedconnection and the apparatus involved station II 0| first initiates thecall and then dials the directory number of the called party subscribersubstation 39|A to 39IJ, inclusive, which numbers are respectively 511to 510, inclusive. Again assuming that the link illustrated is assignedby the distributor II2 for use at this time,- the connector 200 respondsto the numbers 511 to 510, inclusive, in the manner previouslyexplained. More particularly, the first two digits 5 and 1 bring aboutoperation of the wiper carriage of the Strowger mechanism 340 to selectthe party subscriber line 39| to which the party it subscribersubstations 39 IA to 39 IJ, inclusive, and

39|AA to 39IJJ, inclusive, are connected. Whenthe wiper carriage of theStrowger mechanism 340 is operated to its fifth vertical level, the setof switch springs S241 is operated in order to prepare an alternativecircuit traced hereinafter for operating the ring reverse relay R240,The third digit 1 to 0, inclusive, is registered in the code switch 210in order to cause selection of thecorresponding first to tenth,inclusive, ringingacsswsei code conductor extending to the ringing code111- terrupter, not shown Ringing takes place. over the negative linewiper 345 and the negative line. conductor of the party subscriber lineEdi i'l precisely the same manner as that previously ea plained; theringing code on the corresponding first to tenth, inclusive, ringingconductor in turn brings about corresponding'operation of .the ring eratthe corresponding called party subscriber substations 39 IA to 39 IJ,inclusive, in the mannerpreviously explained. When the. subscriber atthe called party subscriber substation 39M. to 39m, inclusive, answersthe call, the ring cut-off relay R230 is operated in order to arrest theprojection of ringing current over the party subscriber line 39L toarrest the return of ring-back tone current to the calling privatesubscriber substation. Tllll and to complete the loop circuit betweenthe called party subscriber substation 391A to 3913 inclusive, and theupper and lower windings of the back-bridge relay REID; whereby anestablished connection is completed between the calling privatesubscriber substation Tit?! and the called party subscriber substation39m to 30M, inclusive. ihe subsequent release or this establishedconnection and the apparatus involved therein is identical to thatpreviously described.

Now assuming that a call is to be extended from the calling private.subscriber substation TIOI to one of the second ten called partysubscriber substations 39IAA to 39IJJ, inclusive,

connected to the party subscriber line 33l in the exchange I0, thesubscriber at the calling private subscriber substation Tifll firstinitiates the call and'then dials thedirectory number of the calledpartysubscriber substation 39IAA to 30iJJ, inclusive, which numbers arerespectively 52i to 520, inclusive. Again assuming that the linkillustrated is assigned by the distributor H2 for use at'this time, theconnector 290 responds to. the numbers 52I. to 520, inclusive, in theman-' ner previously explained. More particularly, the first two digits'5 and 2 bring about operation of the wiper carriage of the Strowgermechanism 3440 again to select the party subscriber line 391 to whichthe party subscriber substations 39IA. to 39IJ, inclusive, and 39|AA to39IJJ, inclusive, are connected; and the set of switch springs S2 i?! isoperated. The third digit 1 to 0, inclusive, is registered in the codeswitch 210 in order to cause the selection of the corresponding first totenth, inclusive, ringing code conductor extend- 7 ing to the ringingcode interrupter, not shown.

tacts 333 and the sets of switch springs S248 and;

S241 and the winding ofthe reverse battery relay R240 to batterypotential. Upon operating the reverse battery relay R240 reverses, atthe con-: tacts 24L 242, 243 and 244, the connections be-. tween thewiper 2' of the code switch 2'10 and ground potential at the contacts H2and the linewipers .34! and 342. More specifically, at this timethewiper 21! of the code switch Z'HIls' connected via the upper winding ofthe ring cut-off relay R230, the contacts 242, 233, 222 and I44 tothe-positive line wiper 342,; and ground'potential. at the contacts I72is connected via the contacts 244,,23l. 221 and IM to they negative linewiper- 3. Accordingly,ringing current'is projected over the positiveline wiper 342 and the positive line conductor of the party subscriberline 39l; whereby the ringer at the called party subscriber substation39lAA, SQEBB, etc., connected between the positive line conductor of theparty subscriber line 39l and ground potential thereat is operateddirectly over the positive line conduc-- tor of the party subscriberline 39 I. For example,

the ringing circuit may extendfrom one terminal of the ringing codeinterrupter, not shown, via the sixth ringing code conductor, the wiper-2.1 I of the code -switch210 and the engaged sixth contact in theassociated contact bank,: the upper winding of the ring cut-off. relayR230, the

contacts 242, 233, 222 and 'l44,'the positive'line' wiper 342, thepositive lineconductor of the partysubscriber line 391- and the ringerin the party:

subscriber substation 39 IFF to ground potential; thence via the sectionof earth between ground potential at the called party subscriber substaetion 39IFF to ground potential in the exchange l0 to which theotherterminal of the ringing code interrupter, not shown; is connected.Subsequently, when the subscriber at the called party subscribersubstation 39IFF answers the call. a circuit substantially identical tothat previously traced'and including the upper winding of the ringcut-off-relay R230 is completed; whereby the latter relay operates inorder to arrest the projection ofringing current over the partysubscr'iber line 391 and the return of ring-back tone current to thecalling private subscriber substa-j tion Tlili, and to complete the loopcircuit between the called party subscriber substation 39IFF and theupper andlower windings of the" back-bridge relay R2l0; whereby 'anestablishedconnection is completed between the calling ,pri-

vate subscriber substation T|0l and the calledpartysubscriber substation39IFF. .The subsequent release of this established connection and theapparatus involved therein is identicalto previously described. 7 Y

In "view of'the foregoing it is apparent that" there has been providedinan automatic tele-j phonersystem, including a group of trunks and aplurality of party subscriber lines, a connector switch incorporatingcombination trunk-huntingand ringing control facility. I

. vWhile there has been described whatisat present. considered to bethe'preferred embodiment of the invention, it will be understood thatvarieous modifications may be made therein, and it is intended tocover-inthe appended claims all such" modifications as fall within thetrue spirit andscopeof the invention. s 7

What is claimed is: I

1. In a telephone system including ,a party subscriber line providedwith first and second line conductors; an automatic switch provided witha contact bank including first and second contact sets commonlyterminating said Party subscriber line, means for selectively operatingsaid switch to select said party subscriber line via said first contactset or via said second con tact set, a ring reverse relay normallyselecting said first line conductor,.said ring reverse/relay beingresponsive to operation of said switch to selectsaid party subscriberline via said secondcontact set to selectsaid second 'line conductor, aringing conductor, andzmeans for connecting. Sa d r ing conductor to theselected one of said line conductors.

that" contact sets commonly terminating said party subscriber line,means for selectively operating said switch to select said partysubscriber line via'said first contact set or via said second con- 5tact set, a ring reverse relay normally selecting said first lineconductor, said ring reverse relay being responsive to operation of saidswitch to select said party subscriber line via said second contactsetto select said second line conductor;

a plurality of ringing conductors, means for selecting any one of saidringing conductors, and means for connecting the selected one of saidringing'conductors to the selected one of said line conductors.

3. In a telephone system including a party ubscriber line provided withfirst and second line conductors; a numerical switch provided with 'acontact bank including first and second "contact sets commonlyterminating said party subscriber line, means responsive to a givendirectory number for operating said switch to select said partysubscriber line via said first contact set and responsive to a differentdirectory number for operating said switch to select said 5 partysubscriber line via said second contact set, a ring reverse relaynormally selecting said first line conductor, said ring reverse relaybeing responsive to operation of said switch to select said partysubscriber line via said second contact set 0 to select said second lineconductor, a ringing conductor, and means for connecting saidringingconductor to the selected one of said line conductors.

4. Ina telephone system, an automatic switch comprising a wiper setincluding first and second line wipers and first and second controlwipers, first and second contact sets accessible to said wiper set andeach including first and second line contacts and first and secondcontrol conm tacts, a line having first and second line conductorsrespectively terminated by the first and second line contacts inbothsaid first andsecond contact sets, a strap connecting together thefirst control contact in said first contact set and the control wiper ofsaid wiper set'a'nd operated in response to the presence of said givenpotential returned upon the second control wiper of said wiper set,means including contacts controlled by said ring reverse relay forselecting the first line wiper of said wiper set when said ringreverserelay occupies, its restored position and for selecting the second linewiper of said wiper set when said ring reverse relay occupies itsoperated position, a ringing conductor, and means for connecting saidringing conductor to the selected one of the line wipers of said wiperset.

6. In a telephone system, an automatic switch comprising a wiper setincluding first and second linewipers and first and second controlwipers, first and second and third contact sets accessible to said wiperset and each including first and second line contacts and first andsecondcontrol contacts, a first line having first and second lineconductors respectively terminated by the first and second line contactsin said first contact set, a first strap connecting together the firstand second control contacts in said first contact set, a second linehaving. first and second line conductors respectively terminated by thefirst and second line contacts in both said second and third contactsets, a second strap connecting together the first control contact insaid second contact set and the first and second control contacts insaid third contact set, means for selectively operating said wiper setto select any one of said contact sets and for applying a givenpotential to the first control wiper of said wiper set, a plurality ofringing codes, mechanism operative to select any one of said ringingcodes, means for selectively operating saidmechanism, means controlledjointly by operation of said wiper set to select said first contact setand by the presence of said given potential returned upon the secondcontrol wiper of saidwiper set and by operation of said mechanism fordetermining the one of the line wipers of said wiper set to which theselected one of said ringing codes is to be connected, and additionalmeans controlled jointly first and second control contacts in Saidsecond by operation of said wiper set to select said seccontact set,means for selectively operating said wiper set to select said firstcontact set or said second contact set and for applying a givenpotential to the first control wiper of said wiper ond contact set orsaid third contact set and by the absence or presence of said givenpotential returned upon the second control wiper of said wiper set fordetermining the one of the line set, a ring reverse relay normallyselecting the wipers said Wiper Set to which the selected one first linewiper of said wiper set, said ring reverse relay being responsive to thepresence of said given potential returned upon the second control wiperof said wiper set to select the second line wiper of said wiper set, aringing conductor, and means for connecting said ringing conductor tothe selected one of the line wipers of said wiper set.

5. In a telephone system, an automatic switch comprising a wiper setincluding first and secon line wipers and first and second controlwipers, first and second contact sets accessible to said wiper set andeach including first and second line contacts and first and secondcontrol contacts, a line having first and second line conductorsrespectively terminated by the first and second line contacts in bothsaid first and second contact sets, a strap connecting together thefirst control contact in said first contact set and the first and secondcontrol contacts in said second contact set, means for selectivelyoperating said wiper set to select said first contact set or said secondcontact set and for applying a given potential to the first controlwiper of said wiper set, a ring reverse relay connected to the second 5ing access to said trunks and to said party subscriber lines andprovided with a pair of line wipers and first and second control wipers,digit responsive means for selectively operating said wiper set toselect the first trunk in said group or any one of said party subscriberlines, a switch-through relay, a test relay, a step relay, a ringcontrol relay, means controlled by operation ofsaid wiper set to makeany selection for completing a test circuit for operating said testrelay over said first control wiper in the event the selected trunk orparty subscriber line is busy, means controlled jointly by operation ofsaid wiper set to select other than the last trunk in said group and byoperation of said test relay for operating said step relay, meanscontrolled by operation of said step relay for restoring said test relayand for reoperating said wiper set to select the next adjacent trunk insaid group, means controlled by sustained operation of said test relayfor returning a busy signal over said switch, means controlled byfailure of operation of said test relay for operating said switchthroughrelay and for preparing a circuit for said ring control relay over saidsecond control wiper, additional means for selectively completing thecircuit for said-ring control relay in the event it is prepared, aringing conductor, and means controlled by the position of said ringcontrol relay for selectively determining the one of the line wipers ofsaid wiper set to which said ringing conductor is to be connected.

8. Inatelephone system including a group of V trunks and a plurality ofparty subscriber lines; an automatic switch comprising a wiper sethaving access to said trunks and to said party subscriber lines andProvided with a pair of line wipers and first and second control wipers,digit responsive means for selectively operating said scriber lines andprovided with a pair-o1 line wiper set to select the first trunk in saidgroup or any one of said party subscriber lines, a switchthrough relay,a test relay, a step relay, a ring control relay, means controlled byoperation of saidwiper setto make any selection for completingatestcircuit for operating said test relay over said first control wiper inthe event the selected trunk or party subscriber line i busy, meanscontrolled jointly by operation of said wipersetto select other than thelast trunk in said group and by operation of said test relay foroperating said step relay, means controlled by operation of said steprelay for restoring said test relay and forreoperating said wiper set to7 select the next adjacent trunk in said group, means controlled bysustained operation of said 'test relay for returning a busy signal oversaid switch, m'eanscontrolled by failure of operation of said test relayfor operating said switchthrough relay and for preparing a circuit forsaid ring control relay over said second control wiper, a plurality ofringing codes, mechanism operative to select any one of said ringingcodes, means for selectivelyoperating said mechanism, means controlledby operation of said mechanism for selectively completing the circuitfor said ring controlrelay in the event it is prepared, and meanscontrolled by the position'of said ring control relay for selectivelydetermining the one of the line wipers of said wiper set to which theselected one of said ringing codes is to be connected;

9. In a telephonesystem including a group'of' trunks and a plurality of'party subscriber lines; an automatic switch comprising a wiper sethaving access to said trunks and to said party subwipersand firstandsecondcontrol wipers, digit responsive means for selectivelyoperating said wiper set to select the first trunk in said group or anyone of said party subscriber lines, a switch-through relay, a testrelay, a step relay, a ring control relay, means controlledby Operationof said wiper set to make any selection for completing a test circuitfor operating said test relay over said first control wiper in the eventthe selected trunk or party subscriber line is busy, means controlledjointly by operation of said wiper set to selectother than the lasttrunk in said group and by operation of said test relay for operatingsaid step relay, means controlled by operation of said step relay forrestoring said test relay and for reoperating said wiperset to selectthe next adjacent trunk in said group,

means controlled by sustained operation of said test relay for returninga busy signal over said switch, means controlled by iailure of operationof said test, relay for operating said switchthrough relay, meanscontrolled by operation of said wiper set to select a particular one ofsaid party subscriber lines for preparing a circuit for said ringcontrol relay over said second control wiper, means controlled byoperation of said switch-through relay for completing said circuit forsaid ring control relay in the event it is prepared, a ringingconductor, and means controlled by the position'oi said ring controlrelay for selectively determining the one of the line wipers of saidwiper set to which said ringing conductor is to be connected.

CLARENCE E. LOM-AX.

REFERENCES CITED The following references are of record in the file ofthis patent: V

UNITED STATES PATENTS Great Britain Dec. 22, 1913

